Leading Causes of Death in Horses

Although completed several years ago, two major studies by the National Animal Health Monitoring System on 'Equine Morbidity and Mortality' describing health problems in the US equine population continue to contain valid information for horse owners in 2016. New window.

Back in 1998, the National Animal Health Monitoring System (NAHMS) did a major study "Equine Morbidity and Mortality" as a priority needs assessment phase to describe health problems in the US equine population. That study was followed up by a study in 2005 to compare changes in the equine industry from 1998 to 2005 in relation to equine deaths.

Since then many studies have been done about individual diseases and conditions that affect the health of equines, and, while many of them give insight into the effects of singular diseases on equine morbidity and mortality, the conclusions of the original two studies in 1998 and 2005 continue to be valid.

In the original study, the USDA collected data on equine health and management practices via personal interviews with a representative sample of equine operations in 28 states.1 The operations represented about three-fourths of the equine population and three-fourths of operations with equine in the US.

For this study, equids were defined as horses, miniature horses, ponies, mules, donkeys, and burros. Overall 2,904 operations with one or more quids participated in the study's interviews. These participants were asked to report the number of various health problems (morbidity) that occurred and the number of and reasons for deaths of equids (Mortality).

The owners/operators were asked for the number of health events that occurred in two age categories of equids, those less than 6 months of age, and those 6 months or older. These health events were reported by the owner/operation and not necessarily confirmed by a veterinarian.

Researchers made these discoveries: Digestive problems other than colic, such as diarrhea at 13.4 percent and injury/wounds/trauma at 12.7 percent affected the largest percentages of operations with equids less than 6 months of age.

For the 6 months or older age group, that largest percentage of operations were affected by injury/sounds/trauma at 17.9 percent, leg and hoof problems at 16 percent and colic at 13.6 percent. Nearly double the percentage of operations had equids affected by obesity compared to chronic weight loss.

Overall, 3.6 percent of foals born alive died at 30 days or less with almost one-half of the deaths occurring in the first 2 days of life. Overall, mortality rates in resident equids over 30 days of age, but less than 6 months compared to those from 6 months up to 5 years, and 5 to 20 years, of age were similar with 1.4 and 1.3 respectively, while the overall mortality rate for those equids 20 years or older was much higher at 11.1 percent.

The largest percentages of foal deaths in those 30 days of age or less were from unknown causes at 33.2 percent, followed by birth defects at 17.6 percent, injury/wounds/trauma at 9.4 percent and birthing problems at 5.1 percent. Other known causes of death included prematurity, lack of milk or colostrum in the mare, exposure or drowning and infection.

By far, the most common cause of death in equids greater than 30 days of ages was old age at 29.5 percent, followed by colic at 17.5 percent and injury/wounds/trauma at 10.5 percent. Injury, wounds, and trauma encompassed cases involving leg/hoof problems and accounted for 17.6 percent of death of equids greater than 30 days of age, a percentage similar to that for colic.

Respiratory problems, injury/wounds/trauma , and leg hoof problems combined accounted for 49.1 percent of deaths in equids from 30 days to 6 months of age.

Colic and injury/sounds/trauma combined with leg or hoof problems accounted for over 50 percent of deaths in the 6 month to 5 year and 5 to 20 year categories.

Overall, only 8.6 percent of deaths in resident equids greater than 30 days of age were of unknown causes compared to 33.2 percent of deaths in foals less than 30 days of age.

Percentage of Operations Where Resident Equids were Affected

Equids 6 Months or Older

Causes

Percentage of Operations

Injury/wounds/trauma

17.9%

Leg/hoof problems

16.0%

Colic

13.6%

Eye problems

7.4%

Respiratory problems

6.3%

Skin problems

6.0%

Overweight/obese

4.5%

Reproductive problems

3.2%

Other digestive problems (e.g., diarrhea)

2.8%

Chronic weight loss

2.7%

Behavioral problems

1.7%

Neurologic problems

1.6%

Generalized infection

1.1%

When it came to number of days of use lost because of disease and conditions, injury/wounds/trauma and leg/hoof problems at 53.4 percent, followed by colic at 16.6 percent and respiratory problems at 7.9 percent accounted for the greatest number of days.

The follow-up study "Trends in Equine Morality, 1998 - 2005 collected data on equine health and management practices from a representative sample of operations with 5 or more equids in 28 states within four regions.2

Participants in the Equine 2005 study were asked to provide information on deaths including euthanasia among their resident equids during the previous 12 months for three age groups: birth to 30 days, 30 days to 6 months, and 6 months and older. Again cause of death was reported by the owner/operator and not necessarily confirmed by a veterinarian.

Foal deaths

Did you know?

Mares secrete colostrum up to 24 hours after foaling. Foals will absorb colostrum for 12 to 24 hours after birth, or until an adequate amount of the whole protein antibodies are absorbed through the small intestine. The quicker we can get the colostrum into the foal, the faster the foal has both systemic and local immunity against disease pathogens.

Overall, the percentages of foals born alive that died witin the first 30 days of life were similar to the earlier study with 4.2 and 4.9 percent respectively. Of these deaths, about hald occurred within the first 2 days of life. For the 2005 study, two new cause-of-death categories were added: infections disease unrelated to specific body system, and flood infection or septicemia. These two new causes of death accounted for 18.2 percent of deaths and the unknown causes of death dropped form 33.2 percent in 1998 to 17.9 percent in 2005, most likely as a result of these two new categories.

In the 2005 study, excluding unknown and other causes of death, injury/wounds/trauma unrelated to birth accounted for the highest percentage of foal deaths at 18.6 percent followed by failure to get colostrum or milk from mare at 14.9 percent and dystocia, trauma, or complications at birth 10.7 percent.

Since injury/wounds/trauma is one of the leading causes of foal deaths during the first 30 days, it may be possible to reduce the overall percentage of deaths in this age category because injury/wound/trauma is a potentially preventable cause of death.

Equid deaths

Overall, the percentages of equids more than 30 days of age that died in 1998 and 2005 were similat at 2.0 and 1.8 respecitively. For equids more than 30 days to less than 6 months of age, the percentages of deaths attributed to a specific cause were similar in 1998 and 2005 with injury/wounds/trauma accounting for the highest percentage of deaths in both studies.

Again, it is hoped that because injury/wounds/trauma deaths are preventable, better management and care can lower the number of deaths in this category.

The most commonly reported causes of death in equids 6 months or older were old age, colic, and injury/wounds/trauma. "Other"known causes of death in 1998 included cancer, percent heart disease, poisoning, lightning strike, liver disease and birth defects. In 2005, "other" known causes of death included heart attack, snake bite, stroke, ruptured vessel, heat stroke, endocrine disease and pigeon fever.

Since a high percentage of deaths among foals aged less than 30 days and equids aged more than 30 days to less than 6 months were attributed to unknown causes in both 1998 and 2005, identifying these unknown causes is an area for further study because if the cause of death is found to be preventable, it may be possible to prevent future equid death from these unknown causes.

The bottom line:

In-depth studies of why horses become ill and die are difficult to find and often focus on major diseases such as West Nile virus and laminitis, but the bottom line is that the causes of horse illnesses and deaths have not changed all that much through recent decades. With many illnesses and deaths attributed to unknown causes it behooves horse owners and equine professionals to engage in the best practices possible to prevent unnecessary illnesses and deaths by being pro-active when it comes to vaccinations, effective parasite control, hoof and dental care, and effective biosecurity measures.

6 Important Take-Aways:

Many illnesses and deaths are preventable, especially those caused by diseases for which vaccines are available and those caused by wounds, injuries, and trauma. Prevention is the key to saving not only lost work days, but also time and money.

Every horse should be on a vaccination and worming schedule based on local area conditions and should rely on their local veterinarian for advice about what and when it is best to vaccinate and deworm their particular horses.

Know your horse's vital signs that can indicate problems with your horse's health. Increased heart rate may be associated with pain or stress. Increased temperature may by associated with infection or disease. In addition, knowing how to take your horse's vital signs is important when communicating important information to your veterinarian.

A daily once-over is the best way to maintain your horse's health. Demeanor, body condition, heat in legs or feet, the horse's attitude and demeanor are all signals of general health. The once-over should be accompanied by a thorough grooming at least once a week.

Develop a good relationship with your veterinarian and farrier. These relationships pay dividends as you learn to take more responsibility for your horse's health. Do not wait until a problem exists to call on these professional service providers. Get to know them in advance and they will provide you with preventative advice that will save you time and money.

Avail yourself of the many educational and informational sources which are often available free of charge such as the AAEP, The Equine Disease Communication Center, State Animal Health Officials and USDA-APHIS-VS, Equine Guelph in Canada and the various state and local colleges with equine health departments in the United States. Many of these educational and informational sources have newsletters and other information available online that can be very helpful to horse owners.

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About the author

EquiMed Staff shares a common goal of helping you improve your horse's health. The staff work together to develop unique web-focused content that answers the most common questions of horse owners. EquiMed staff written content is updated frequently to incorporate the best practices within the equine healthcare industry. Thanks for visiting!